WO2012105628A1 - Wavelength dispersion amount estimation method, wavelength dispersion compensation circuit, and reception device - Google Patents

Wavelength dispersion amount estimation method, wavelength dispersion compensation circuit, and reception device Download PDF

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Publication number
WO2012105628A1
WO2012105628A1 PCT/JP2012/052318 JP2012052318W WO2012105628A1 WO 2012105628 A1 WO2012105628 A1 WO 2012105628A1 JP 2012052318 W JP2012052318 W JP 2012052318W WO 2012105628 A1 WO2012105628 A1 WO 2012105628A1
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Prior art keywords
dispersion compensation
amount
clock detection
detection value
compensation amount
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PCT/JP2012/052318
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French (fr)
Japanese (ja)
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山崎　悦史
小林　孝行
富沢　将人
理一 工藤
浩一 石原
中川　匡夫
光映 石川
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日本電信電話株式会社
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Application filed by 日本電信電話株式会社 filed Critical 日本電信電話株式会社
Priority to US13/982,507 priority Critical patent/US8971703B2/en
Priority to JP2012555941A priority patent/JP5663606B2/en
Priority to CN201280007278.0A priority patent/CN103404051B/en
Publication of WO2012105628A1 publication Critical patent/WO2012105628A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/616—Details of the electronic signal processing in coherent optical receivers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
    • G01M11/338—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face by measuring dispersion other than PMD, e.g. chromatic dispersion
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
    • H04B10/0795—Performance monitoring; Measurement of transmission parameters
    • H04B10/07951—Monitoring or measuring chromatic dispersion or PMD

Definitions

  • the present invention is used in optical communication, and a chromatic dispersion amount estimation method for compensating for waveform distortion caused by chromatic dispersion, interpolarization interference, polarization mode dispersion, etc. in an optical fiber transmission line using digital signal processing, and chromatic dispersion
  • the present invention relates to a compensation circuit and a receiving device.
  • Non-Patent Documents 1 and 2 compensates for quasi-static chromatic dispersion with a fixed digital filter (for example, for a 28 Gbaud signal, the dispersion is 20000 ps / nm and the number of taps is 2048 tap).
  • a method is adopted in which the polarization mode dispersion with fluctuation is compensated with an adaptive filter having a small number of taps (for example, about 10 to 12 taps with a polarization mode dispersion of 50 ps) using a blind algorithm.
  • the amount of chromatic dispersion received in the transmission line includes various types of transmission line fibers such as a single mode fiber, a dispersion shifted fiber, and a non-zero dispersion shifted fiber. Further, since the cumulative chromatic dispersion amount increases in proportion to the length of the transmission line fiber through which the signal light has propagated, the cumulative dispersion amount also changes depending on the transmission distance. In some cases, an optical dispersion compensator is inserted in the repeater of the transmission system, and the residual dispersion amount changes depending on the compensation amount.
  • a dispersion compensating fiber may be used as a transmission line.
  • the chromatic dispersion coefficient varies depending on the carrier wavelength of the signal light
  • the accumulated dispersion amount also depends on the signal light wavelength.
  • the coefficient of the dispersion compensation filter should be controlled at the receiving end in accordance with the accumulated chromatic dispersion amount. Therefore, a mechanism for estimating the accumulated chromatic dispersion received by the signal is required.
  • the estimated value of chromatic dispersion is set as the compensation amount for the dispersion compensation circuit, if there is an error between the value to be actually compensated and the estimated value, waveform distortion due to chromatic dispersion remains after compensation and the error rate is increased. End up.
  • the tolerance to distortion factors other than chromatic dispersion, such as polarization mode dispersion is reduced. Therefore, it is important to reduce the error of the chromatic dispersion compensation amount in order to operate the optical transmission system stably and with high reliability.
  • the present invention provides a chromatic dispersion amount estimation that estimates and sets a chromatic dispersion amount to be compensated at high speed and with high accuracy in a receiver that compensates for waveform distortion in an optical fiber transmission line. It is an object to provide a method, a chromatic dispersion compensation circuit, and a receiving apparatus.
  • a chromatic dispersion amount estimation method includes: (1) A step of setting an arbitrary value as a first candidate value of the chromatic dispersion amount; (2) extracting a plurality of neighborhood values of the first candidate values as second candidate values; (3) measuring a digital clock extraction signal intensity corresponding to each candidate value; (4) extracting an optimum value (maximum value) from a plurality of signal intensity increasing / decreasing trends and setting it as the next first candidate value; (5) A determination step that repeats (2) to (4) until a predetermined condition is satisfied, It was decided to have.
  • the chromatic dispersion amount estimation method is a chromatic dispersion amount estimation method for estimating a dispersion compensation amount when compensating for waveform distortion due to chromatic dispersion of an optical fiber transmission line,
  • An initial value setting procedure for setting a dispersion compensation amount D (0) that is an initial value (k 0) of the kth (k is an integer) th dispersion compensation amount D (k);
  • the dispersion compensation amount D (k) is a predetermined amount [Delta] D of M (k-1) worth of 1 (M is one or more real) dispersion compensation amount is shifted to the positive side by D (k) + ⁇ D / M (k-1 ) In which the symbol arrival timing clock is detected as a clock detection value S (k +) and stored.
  • the optimal dispersion compensation amount can be obtained by comparing the clock detection value in the comparison procedure and adjusting the dispersion compensation amount in the direction in which the clock detection value increases. Further, by setting the second candidate value in step (2) close to the first candidate value according to the number of trials, overshooting can be avoided and the chromatic dispersion amount can be estimated at high speed and with high accuracy. be able to.
  • the present invention can provide a chromatic dispersion amount estimation method for estimating and setting a chromatic dispersion amount to be compensated at high speed and with high accuracy in a receiver that compensates for waveform distortion in an optical fiber transmission line.
  • the chromatic dispersion amount estimation method acquires an approximate value of the dispersion compensation amount before the initial value setting procedure, and uses the approximate value of the dispersion compensation amount as the dispersion compensation amount D ( And 0) having an approximate dispersion compensation amount acquisition procedure.
  • a rough estimated value estimated by a chromatic dispersion estimation method using a known signal is set as an initial value of the dispersion compensation amount.
  • the chromatic dispersion amount estimation method according to the present invention is characterized in that at least one of the clock detection procedure, the plus shift procedure, and the minus shift procedure is averaged by repeating a plurality of times at different times.
  • a minute amount ⁇ D smaller than the predetermined amount ⁇ D for shifting the dispersion compensation amount in the plus side shift procedure and the minus side shift procedure is set.
  • the dispersion compensation amount centering on the clock detection value S (k ⁇ 0 +) and the dispersion compensation amount D (k) + ⁇ D in the dispersion compensation amount D (k) + ⁇ D / M (k ⁇ 1) D (k) + ⁇ D / M (k ⁇ 1) ⁇ n ⁇ D (where n is a natural number) detects a clock detection value S (k ⁇ n ⁇ +),
  • the clock detection value S (k ⁇ 0) and the clock detection value S (k ⁇ n ⁇ ) are averaged to obtain the clock detection value S (k)
  • the clock detection value S (k ⁇ 0 +) and the clock detection value S (k ⁇ n ⁇ +) are averaged to obtain the clock detection value S (k +)
  • the clock detection value S (k ⁇ 0 ⁇ ) and the clock detection value S (k ⁇ n ⁇ ) are averaged to obtain the clock detection value S (k ⁇ ).
  • the difference between the clock detection value S (k) and the clock detection value S (k +) and the clock detection value S (k) and the clock detection value are determined.
  • the difference from S (k ⁇ ) is less than a predetermined threshold, the dispersion compensation amount D (k) is determined as the optimum dispersion compensation amount, and the estimation of the dispersion compensation amount is completed.
  • the estimation operation can be stabilized by avoiding estimation in a state where the difference between the clock detection values is small and the optimum value is in an uncertain state.
  • the chromatic dispersion compensation circuit is an analog-digital converter that converts an optical analog waveform received from the optical fiber transmission line into a digital signal;
  • a digital signal processor that compensates for waveform distortion due to chromatic dispersion of the optical fiber transmission line of the digital signal output by the analog-digital converter with the dispersion compensation amount estimated by the chromatic dispersion amount estimation method;
  • a symbol clock extractor that extracts a symbol arrival timing clock of received data included in the digital signal output by the analog-digital converter and outputs the intensity of the symbol arrival timing clock as the clock detection value; Is provided.
  • the chromatic dispersion compensation circuit according to the present invention employs the chromatic dispersion amount estimation method. Therefore, the present invention can provide a chromatic dispersion compensation circuit that estimates and sets the amount of chromatic dispersion to be compensated at high speed and with high accuracy in a receiver that compensates for waveform distortion in an optical fiber transmission line.
  • the receiving apparatus includes the chromatic dispersion compensation circuit.
  • a receiving apparatus includes the chromatic dispersion compensation circuit. Therefore, the present invention can provide a receiving apparatus that compensates for waveform distortion in an optical fiber transmission line and estimates and sets the amount of chromatic dispersion to be compensated at high speed and with high accuracy.
  • the present invention relates to a chromatic dispersion amount estimating method, a chromatic dispersion compensation circuit, and a receiving apparatus for estimating and setting a chromatic dispersion amount to be compensated at high speed and with high accuracy in a receiving apparatus for compensating waveform distortion in an optical fiber transmission line. Can be provided.
  • FIG. 5 is a diagram illustrating the receiving device 300 according to the present embodiment.
  • the receiving apparatus 300 includes a chromatic dispersion compensation circuit 101.
  • the chromatic dispersion compensation circuit 101 is based on an analog-digital converter 11 that converts an optical analog waveform received from an optical fiber transmission path into a digital signal, and wavelength dispersion of the optical fiber transmission path that the digital signal output from the analog-digital converter 11 has.
  • a digital signal processor 12 that compensates for waveform distortion with a dispersion compensation amount estimated by a chromatic dispersion amount estimation method described below, and a symbol arrival timing clock of received data included in the digital signal output from the analog-digital converter 11 And a symbol clock extractor 13 for extracting and outputting the intensity of the symbol arrival timing clock as a clock detection value.
  • a rough estimation value estimated by a chromatic dispersion estimation method using a known signal or the like is set as an initial value in the dispersion compensation circuit.
  • a waveform subjected to waveform distortion due to residual dispersion caused by an estimation error or the like is output from the dispersion compensation circuit.
  • D (k) represents the dispersion compensation amount set in the digital signal processor 12.
  • S (0) a clock detection value
  • the dispersion compensation amount D (0) is shifted in a negative direction by a certain shift amount ⁇ D (dispersion compensation amount D (0) ⁇ ), and the clock detection value S ( Measure and store 0-).
  • the constant shift amount ⁇ D is about the maximum value of the deviation amount from the expected value of the initial value.
  • the initial value depends on the rough estimation algorithm to be used (for example, the algorithm of Patent Document 4). For example, assuming that the error is 1.5 to 5% of the dispersion amount 20000 psec / nm exemplified as the compensation range in Patent Document 4, ⁇ D is set to 300 to 1000 psec / nm.
  • the shift amount ⁇ D / 4 is shifted in the positive and negative directions around the compensation dispersion amount D (2) [5] [6].
  • the respective clock synchronization detection signals S (2+) and S (2-) when the dispersion compensation amount is shifted to positive and negative are detected and stored in the memory. Then, both are compared and shifted in a larger code direction. Thereafter, by repeating the same process, the optimum compensation dispersion amount can be made asymptotic.
  • the shift amount of the compensation dispersion amount D (k) at the k-th stage is ⁇ D / (2 (k ⁇ 1) ), and is halved each time the process proceeds.
  • the detection signal originally includes an error
  • S (k) is set again.
  • S (k) is set again.
  • shifting based on uncertain information can reduce the risk of causing an unstable operation.
  • the shift amount of the compensation dispersion amount D (k) is halved for each step, that is, ⁇ D / (2 (k ⁇ 1) ), but the shift amount is ⁇ D / (M (k ⁇ 1) ) ) (M is a real number of 1 or more).
  • the dispersion compensation amount setting value is determined based on one measurement value of the clock detection signal at each setting value. Therefore, when the error of S (k) in each measurement is large, the optimization sequence may be unstable.
  • a method for stabilization measure multiple times at different times for each set value, and compare the average value to determine which direction of positive or negative sign should be used for stable operation. Is expected.
  • the coarse estimation value of the dispersion estimation circuit is used as the initial value of the dispersion compensation amount.
  • a dispersion value given from the outside may be set.
  • a case where the dispersion amount of the transmission line is previously measured with a dispersion measuring device or the like can be considered.
  • FIG. 3 is a diagram for explaining the fine adjustment process of the present embodiment.
  • a coarse compensation dispersion compensation amount D (0) estimated by a chromatic dispersion estimation method using a known signal or the like is set as an initial value in the dispersion compensation circuit.
  • most of the chromatic dispersion is compensated, and a waveform subjected to waveform distortion due to residual dispersion caused by an estimation error or the like is output from the dispersion compensation circuit.
  • the clock-synchronized clock detection value S (0) at the initially set dispersion compensation amount D (0) is measured and stored.
  • the dispersion compensation set value is shifted in the positive direction by a small amount ⁇ D from D (0) as the first step.
  • the clock detection value S (0 + ⁇ ) synchronized with the clock is measured and stored. Further, shifting in the positive direction by ⁇ D, and measuring clock-synchronized clock detection values S (0 + 2 ⁇ ), S (0 + 3 ⁇ ),..., S (0 + n ⁇ ) at the points 2 ⁇ D, 3 ⁇ D,. It may be stored in a memory.
  • ⁇ D is shifted in the negative direction, and the clock detection value S (0 ⁇ ) of the clock synchronization at that time is measured and stored in the memory. Similarly, it is shifted in the negative direction by ⁇ D, and at the points ⁇ 2 ⁇ D, ⁇ 3 ⁇ D,..., The clock detection values S (0-2 ⁇ ), S (0-3 ⁇ ),. S (0 ⁇ n ⁇ ) may be measured and stored in the memory.
  • a control block diagram of this part is shown in FIG. Repeat this N times.
  • an example in which the number of equal points is measured with respect to positive and negative is shown, but it is not necessary to be particularly equal to positive and negative. For example, only D (0) and D (0) + ⁇ D may be measured.
  • the minute amount ⁇ D is set based on the period and amplitude of the ripple generated in the clock detection value S (k) with respect to the dispersion compensation amount in FIG. Specifically, the minute amount ⁇ D may be set to be equal to or less than the ripple period. For example, when the amplitude of the ripple is about 10% of the clock detection value S (k), the average fluctuation amount of the clock detection value S (k) when the set dispersion compensation amount D (k) is shifted by ⁇ D is the clock. It is less than 10% of the detected value S (k). When the ripple period changes depending on conditions, the minute amount ⁇ D is made sufficiently smaller than the standard deviation of the final target error.
  • ⁇ D can be set to 1/3 to 1/50 of the target error, preferably 1/5 to 1/20, and more preferably 1/7 to 1/20.
  • the final target error is 50 psec / nm to 150 psec / nm
  • ⁇ D is set to about 1 psec / nm to 50 psec / nm, preferably about 4 psec / nm to 30 psec / nm.
  • ⁇ D when ⁇ D is changed according to k, it is changed to ⁇ D / (2 (k ⁇ 1) ) similarly to ⁇ D.
  • ⁇ D can be set to 1/3 to 1/50 of ⁇ D, preferably 1/5 to 1/10, and more preferably 1/5 to 1/7.
  • n.delta. +) and S (0. ⁇ .n.delta.-) are compared to comprehensively determine the sign direction in which the clock synchronization detection signal becomes large, and the dispersion compensation value is shifted.
  • S (0 ⁇ n ⁇ ), S (0 ⁇ n ⁇ +), and S (0 ⁇ n ⁇ ) are averaged with respect to n, and each average value Savg (0) , Savg (0+), Savg (0 ⁇ ) are calculated.
  • N is also set in consideration of the balance between accuracy and time.
  • ⁇ D is fixed, it is limited by the relationship between ⁇ D and ⁇ D. If ⁇ D> ⁇ D / (2 (N ⁇ 1) ), the error cannot be reduced.
  • N is set to 3 or more and 7 or less.
  • the dispersion compensation amount D (1) is set to D (0) + ⁇ D.
  • the dispersion compensation amount D (1) is set to D (0) ⁇ D.
  • both Savg (0+) and Savg (0 ⁇ ) are smaller than Savg (0), it may be considered that Savg (0)> Savg (0+) and Savg (0)> Savg (0 ⁇ ).
  • Is D (1) D (0).
  • the control method after the second stage is the clock detection value at the point of dispersion compensation amount D (1), the point of D (1) + ⁇ D / 2, and the point of D (1) ⁇ D / 2.
  • the positive / negative shift direction is performed using ⁇ D shifted in the positive / negative direction near each point and using the averaged clock detection values. Determine the direction.
  • the dispersion compensation amount is shifted in the positive direction by the shift amount ⁇ D / 2 [1], and the dispersion compensation amount D (1) + ⁇ D / 2 is shifted in the positive and negative directions by a small amount n ⁇ ⁇ D to detect the clock.
  • the value S (1 ⁇ n ⁇ +) is acquired [7] [8].
  • Savg (1+) subjected to the averaging process is obtained.
  • the dispersion compensation amount is shifted by a shift amount ⁇ D / 2 in the negative direction [2]
  • the dispersion compensation amount D (1) ⁇ D / 2 is shifted by a minute amount n ⁇ ⁇ D in the positive and negative directions around the center.
  • the clock detection value S (1 ⁇ n ⁇ ) is acquired. Further, using the detected values, Savg (1-) subjected to the averaging process is obtained.
  • the positive / negative shift direction of the compensation dispersion amount is determined in the same manner as described above.
  • a point where the compensation dispersion amount is D (2) a point shifted by a shift amount ⁇ D / 4 in the positive and negative directions around D (2), and these three points D (2) D (2) + ⁇ D / 4 D (2) - ⁇ D / 4 Comparison of the clock detection value at.
  • the shift amount is further halved to ⁇ D / 4.
  • S (1 ⁇ n ⁇ +) S (1 ⁇ n ⁇ -) To get.
  • the average value Save (2) of these Savg (2+) Savg (2-) As described in the second step, the shift direction of the next step is determined.
  • the optimum compensation dispersion amount can be made asymptotic.
  • the shift amount at the k-th stage is ⁇ D / (2 (k ⁇ 1) ), which is halved as the process proceeds.
  • the example in which the shift amount of the compensation dispersion amount D (k) is reduced by half, that is, ⁇ D / (2 (k ⁇ 1) ) has been described.
  • the shift amount is ⁇ D as in the first embodiment. / (M (k-1) ).
  • the minute amount for the averaging process is a constant value of ⁇ D. .
  • the dispersion compensation amount cannot be optimized in units smaller than ⁇ D. Therefore, as the shift amount is halved to ⁇ D, ⁇ D / 2, ⁇ D / 4,...
  • the minute amount ⁇ D may be reduced within a range where the averaging is effective. For example, the minute amount may be changed as small as ⁇ D, ⁇ D / 2, ⁇ D / 4,.
  • a minute change is given to the compensation amount of the chromatic dispersion compensation circuit of the optical communication system, and this is given when searching for the optimum compensation amount using the clock detection signal as a monitor signal.
  • the optimum dispersion compensation amount can be efficiently detected by reducing the change amount by half for each trial.

Abstract

The objective of the present invention is to provide a wavelength dispersion amount estimation method to rapidly and precisely estimate and set a wavelength dispersion amount to be compensated in a reception device for compensating for waveform distortion in an optical fiber transmission path, and to provide a wavelength dispersion compensation circuit, and a reception device. This wavelength dispersion compensation circuit (101) is provided with: an analog-digital converter (11) which converts optical analog waveforms received from an optical fiber transmission path to digital signals; a digital signal processor (12) which compensates for waveform distortions of the digital signals output from the analog-digital converter (11) due to the wavelength dispersion in the optical fiber transmission path, with the dispersion compensation amount estimated by the wavelength dispersion amount estimation method; and a symbol clock extractor (13) which extracts symbol arrival timing clocks of the reception data contained in the digital signals output from the analog-digital converter (11), and outputs the intensities of the symbol arrival timing clocks as the clock detection values.

Description

波長分散量推定方法、波長分散補償回路、及び受信装置Chromatic dispersion amount estimation method, chromatic dispersion compensation circuit, and receiver
　本発明は，光通信において用いられるものであり、光ファイバ伝送路における波長分散、偏波間干渉、偏波モード分散などによる波形歪みをデジタル信号処理を用いて補償する波長分散量推定方法、波長分散補償回路、及び受信装置に関する。 The present invention is used in optical communication, and a chromatic dispersion amount estimation method for compensating for waveform distortion caused by chromatic dispersion, interpolarization interference, polarization mode dispersion, etc. in an optical fiber transmission line using digital signal processing, and chromatic dispersion The present invention relates to a compensation circuit and a receiving device.
　光通信の分野において、周波数利用効率を飛躍的に向上する同期検波方式と信号処理を組み合わせた通信システムが注目されている。直接検波により構築されていたシステムと比較すると、受信感度を向上することができるだけでなく、デジタル信号として受信することで、光ファイバ伝送によって受ける波長分散、偏波モード分散による送信信号の波形歪みを補償することができることが知られており、次世代の光通信技術として導入が検討されている。 In the field of optical communication, a communication system that combines signal processing with a synchronous detection method that dramatically improves frequency utilization efficiency has attracted attention. Compared with a system built by direct detection, not only can the reception sensitivity be improved, but also by receiving it as a digital signal, the waveform distortion of the transmitted signal due to chromatic dispersion and polarization mode dispersion received by optical fiber transmission can be reduced. It is known that it can be compensated, and its introduction as a next-generation optical communication technology is being studied.
　非特許文献１および２に代表されるデジタルコヒーレント方式は、準静的な波長分散を固定のデジタルフィルタ（例えば、２８Ｇｂａｕｄの信号に対し、２００００ｐｓ／ｎｍの分散でタップ数が２０４８ｔａｐ）で補償し、変動のある偏波モード分散を、ブラインドアルゴリズムを用いた小さいタップ数（例えば、５０ｐｓの偏波モード分散で１０～１２ｔａｐ程度）の適応フィルタで補償する方法を採用している。 The digital coherent system represented by Non-Patent Documents 1 and 2 compensates for quasi-static chromatic dispersion with a fixed digital filter (for example, for a 28 Gbaud signal, the dispersion is 20000 ps / nm and the number of taps is 2048 tap). A method is adopted in which the polarization mode dispersion with fluctuation is compensated with an adaptive filter having a small number of taps (for example, about 10 to 12 taps with a polarization mode dispersion of 50 ps) using a blind algorithm.
特開２００１－０５３６７９号公報JP 2001-053679 A ＷＯ／２００９／１４４９９７パンフレットWO / 2009/144997 Brochure 特願２００９－１６９５１８号公報Japanese Patent Application No. 2009-169518 ＷＯ／２０１１／００７８０３パンフレットWO / 2011/007803 Brochure
　伝送システムでは、受信端において伝送路で付加された波長分散による波形歪みを、受信端のデジタル信号処理によって補償する。このとき、伝送路において受ける波長分散量は、伝送路ファイバには、シングルモードファイバ、分散シフトファイバ、ノンゼロ分散シフトファイバなどの種類があり、信号が受ける単位長さあたりの波長分散量が異なる。また、信号光が伝搬した伝送路ファイバの長さに比例して、累積波長分散量が増加するため、伝送距離によっても累積分散量が変化する。また、伝送システムの中継器において光分散補償器を挿入する場合もあり、その補償量によって残留分散量が変化する。また、海底システムなどでは、分散補償ファイバを伝送路として用いる場合もある。さらに、信号光のキャリア波長によって、波長分散係数が異なるため、累積分散量は信号光波長にも依存する。上記の理由により、受信端では累積波長分散量に合わせて、分散補償フィルタの係数を制御すべきである。したがって、信号が受けた累積波長分散量を推定する機構が必要になる。 In the transmission system, waveform distortion due to chromatic dispersion added in the transmission path at the receiving end is compensated by digital signal processing at the receiving end. At this time, the amount of chromatic dispersion received in the transmission line includes various types of transmission line fibers such as a single mode fiber, a dispersion shifted fiber, and a non-zero dispersion shifted fiber. Further, since the cumulative chromatic dispersion amount increases in proportion to the length of the transmission line fiber through which the signal light has propagated, the cumulative dispersion amount also changes depending on the transmission distance. In some cases, an optical dispersion compensator is inserted in the repeater of the transmission system, and the residual dispersion amount changes depending on the compensation amount. Further, in a submarine system, a dispersion compensating fiber may be used as a transmission line. Furthermore, since the chromatic dispersion coefficient varies depending on the carrier wavelength of the signal light, the accumulated dispersion amount also depends on the signal light wavelength. For the above reasons, the coefficient of the dispersion compensation filter should be controlled at the receiving end in accordance with the accumulated chromatic dispersion amount. Therefore, a mechanism for estimating the accumulated chromatic dispersion received by the signal is required.
　最適な波長分散補償量を検出する従来技術としては、波長分散による波形歪みが残留することで発生する受信信号品質の劣化する特徴を用いる方法がある。例えば、波長分散による残留波形歪みは誤り率を増大させる。従って、例えば既知信号パターンと受信パターンを比較して誤り率を算出し、その値が低くなるように波長分散補償回路への設定値を制御する方法がある。また、一般に波長分散による波形歪みが残留する場合、クロック抽出・同期回路における同期検出信号が小さくなる。この特徴を利用することで、波長分散補償量を制御する方法がある（例えば、特許文献１を参照。）。また、アイパターンの開口度を利用する方法も提案されている（例えば、特許文献２を参照。）。 As a conventional technique for detecting an optimum amount of chromatic dispersion compensation, there is a method using a feature that deteriorates received signal quality caused by waveform distortion due to chromatic dispersion remaining. For example, residual waveform distortion due to chromatic dispersion increases the error rate. Therefore, for example, there is a method of calculating the error rate by comparing the known signal pattern and the reception pattern, and controlling the set value to the chromatic dispersion compensation circuit so that the value becomes low. In general, when waveform distortion due to chromatic dispersion remains, the synchronization detection signal in the clock extraction / synchronization circuit becomes small. There is a method for controlling the amount of chromatic dispersion compensation by utilizing this feature (see, for example, Patent Document 1). In addition, a method using the opening degree of the eye pattern has been proposed (see, for example, Patent Document 2).
　しかし、これらの方法では、受信信号が受けてきた累積波長分散量と、分散補償回路における補償量が大きく異なる場合には、補償の残留分散量とモニタ信号変化との相関が極端に低くなり、モニタ信号を用いて分散補償量を制御することが不可能である。そのため、残留分散量とモニタ信号の相関が得られるような残留分散量となるように、網羅的に分散補償量を変化させて掃引するなどのプロセスが必要であり、設定時間が長くなる問題があった。 However, in these methods, when the accumulated chromatic dispersion amount received by the received signal and the compensation amount in the dispersion compensation circuit are greatly different, the correlation between the residual dispersion amount of compensation and the monitor signal change becomes extremely low, It is impossible to control the dispersion compensation amount using the monitor signal. For this reason, a process such as sweeping by changing the dispersion compensation amount exhaustively is required so that the residual dispersion amount can obtain a correlation between the residual dispersion amount and the monitor signal. there were.
　一方、高速に補償すべき波長分散量を検知する方法として、既知信号を送信信号光に挿入して、既知信号の波形変化から受信端において既知信号部分を利用して波長分散量を推定する方法などがある（例えば、特許文献３を参照。）。 On the other hand, as a method of detecting the amount of chromatic dispersion to be compensated at high speed, a method of estimating the chromatic dispersion amount by inserting a known signal into the transmission signal light and using the known signal portion at the receiving end from the waveform change of the known signal (For example, refer to Patent Document 3).
　しかしながら、既知信号を用いた分散推定法は高速であるが、偏波モード分散、非線形波形歪みなど波長分散以外の波形歪みによって推定量に誤差が生じてしまう問題があった。 However, although the dispersion estimation method using a known signal is high speed, there is a problem that an error occurs in the estimation amount due to waveform distortion other than chromatic dispersion such as polarization mode dispersion and nonlinear waveform distortion.
　分散補償回路に対して波長分散の推定値を補償量として設定すると、実際補償すべき値と推定値に誤差があった場合、補償後にも波長分散による波形歪みが残留し、誤り率を増加させてしまう。また、例えば偏波モード分散など波長分散以外の歪み要因に対する耐力を低減させてしまう。従って、波長分散補償量の誤差を低減することが光伝送システムを安定且つ高信頼に運用するために重要になる。 When the estimated value of chromatic dispersion is set as the compensation amount for the dispersion compensation circuit, if there is an error between the value to be actually compensated and the estimated value, waveform distortion due to chromatic dispersion remains after compensation and the error rate is increased. End up. In addition, the tolerance to distortion factors other than chromatic dispersion, such as polarization mode dispersion, is reduced. Therefore, it is important to reduce the error of the chromatic dispersion compensation amount in order to operate the optical transmission system stably and with high reliability.
　上記で示したように、モニタ信号を用いた制御では検出までに長時間を要すること、また、既知信号を用いた分散推定法では推定誤差の発生を考慮する必要があること、という課題があった。 As described above, there is a problem that control using a monitor signal requires a long time until detection, and that a variance estimation method using a known signal needs to consider generation of an estimation error. It was.
　そこで、前記課題を解決するために、本発明は、光ファイバ伝送路における波形歪みを補償する受信装置において、補償すべき波長分散量を高速に、かつ高精度に推定及び設定する波長分散量推定方法、波長分散補償回路、及び受信装置を提供することを目的とする。 Accordingly, in order to solve the above-mentioned problems, the present invention provides a chromatic dispersion amount estimation that estimates and sets a chromatic dispersion amount to be compensated at high speed and with high accuracy in a receiver that compensates for waveform distortion in an optical fiber transmission line. It is an object to provide a method, a chromatic dispersion compensation circuit, and a receiving apparatus.
　上記目的を達成するために、本発明に係る波長分散量推定方法は、
（１）任意の値を波長分散量の第１の候補値とするステップ、
（２）第１の候補値の近傍値を第２の候補値として複数抽出するステップ、
（３）各候補値に対応するデジタルクロック抽出信号強度を測定するステップ、
（４）複数の信号強度の増減の傾向から最適値（最大となる値）を抽出し、次の第１の候補値とするステップ、
（５）所定の条件を満たすまで、（２）～（４）を繰り返す判定ステップ、
を有することとした。 In order to achieve the above object, a chromatic dispersion amount estimation method according to the present invention includes:
(1) A step of setting an arbitrary value as a first candidate value of the chromatic dispersion amount;
(2) extracting a plurality of neighborhood values of the first candidate values as second candidate values;
(3) measuring a digital clock extraction signal intensity corresponding to each candidate value;
(4) extracting an optimum value (maximum value) from a plurality of signal intensity increasing / decreasing trends and setting it as the next first candidate value;
(5) A determination step that repeats (2) to (4) until a predetermined condition is satisfied,
It was decided to have.
　具体的には、本発明に係る波長分散量推定方法は、光ファイバ伝送路の波長分散による波形歪みを補償する際の分散補償量を推定する波長分散量推定方法であって、
　第ｋ（ｋは整数）番目の分散補償量Ｄ（ｋ）の初期値（ｋ＝０）である分散補償量Ｄ（０）を設定する初期値設定手順と、
　受信データに含まれるシンボル到来タイミングクロックの分散補償量Ｄ（ｋ）における強度をクロック検出値Ｓ（ｋ）として検出し、記憶するクロック検出手順と、
　前記分散補償量Ｄ（ｋ）を所定量ΔＤのＭ（ｋ－１）分の１（Ｍは１以上の実数）だけプラス側にシフトした分散補償量Ｄ（ｋ）＋ΔＤ／Ｍ（ｋ－１）における前記シンボル到来タイミングクロックの強度をクロック検出値Ｓ（ｋ＋）として検出し、記憶するプラス側シフト手順と、
　前記分散補償量Ｄ（ｋ）を所定量ΔＤのＭ（ｋ－１）分の１だけマイナス側にシフトした分散補償量Ｄ（ｋ）－ΔＤ／Ｍ（ｋ－１）における前記シンボル到来タイミングクロックの強度をクロック検出値Ｓ（ｋ－）として検出し、記憶するマイナス側シフト手順と、
　前記クロック検出値Ｓ（ｋ）、前記クロック検出値Ｓ（ｋ＋）及び前記クロック検出値Ｓ（ｋ－）を比較する比較手順と、
　前記比較手順の結果、前記クロック検出値Ｓ（ｋ）が最大である場合、前記分散補償量Ｄ（ｋ）を最適分散補償量として決定して前記分散補償量の推定を完了し、前記クロック検出値Ｓ（ｋ＋）又は前記クロック検出値Ｓ（ｋ－）が最大である場合、最大の前記クロック検出値の前記分散補償量を第ｋ＋１番目の分散補償量Ｄ（ｋ＋１）として前記クロック検出手順、前記プラス側シフト手順、前記マイナス側シフト手順及び前記比較手順を再度行うことを決定する判定手順と、
を行うことを特徴とする。 Specifically, the chromatic dispersion amount estimation method according to the present invention is a chromatic dispersion amount estimation method for estimating a dispersion compensation amount when compensating for waveform distortion due to chromatic dispersion of an optical fiber transmission line,
An initial value setting procedure for setting a dispersion compensation amount D (0) that is an initial value (k = 0) of the kth (k is an integer) th dispersion compensation amount D (k);
A clock detection procedure for detecting and storing the intensity at the dispersion compensation amount D (k) of the symbol arrival timing clock included in the received data as the clock detection value S (k);
The dispersion compensation amount D (k) is a predetermined amount [Delta] D of M (k-1) worth of 1 (M is one or more real) dispersion compensation amount is shifted to the positive side by D (k) + ΔD / M (k-1 ) In which the symbol arrival timing clock is detected as a clock detection value S (k +) and stored.
The symbol arrival timing clock at a dispersion compensation amount D (k) −ΔD / M (k−1) obtained by shifting the dispersion compensation amount D (k) to the minus side by a factor of M (k−1 ) of the predetermined amount ΔD. A negative shift procedure for detecting and storing the detected intensity as a clock detection value S (k−);
A comparison procedure for comparing the clock detection value S (k), the clock detection value S (k +) and the clock detection value S (k−);
If the clock detection value S (k) is the maximum as a result of the comparison procedure, the dispersion compensation amount D (k) is determined as the optimum dispersion compensation amount, and the estimation of the dispersion compensation amount is completed, and the clock detection When the value S (k +) or the clock detection value S (k−) is the maximum, the clock detection procedure with the dispersion compensation amount of the maximum clock detection value as the (k + 1) th dispersion compensation amount D (k + 1), A determination procedure for determining to perform the plus shift procedure, the minus shift procedure, and the comparison procedure again;
It is characterized by performing.
　ある分散補償量のクロック検出値とその前後の分散補償量のクロック検出値とを比較したとき、クロック検出値が大きい分散補償量の方向に最適クロック検出値、すなわち最適分散補償量が存在すると考えられる。このため、比較手順でクロック検出値を比較し、クロック検出値が大きくなる方向へ分散補償量を調整することで、最適分散補償量を得ることができる。さらに、ステップ（２）の第２の候補値を試行回数に応じて第１の候補値の近くに設定していくことで、オーバーシューティングを回避し、波長分散量を高速かつ高精度に推定することができる。 When comparing the clock detection value of a certain dispersion compensation amount with the clock detection value of the dispersion compensation amount before and after that, it is considered that the optimum clock detection value, that is, the optimum dispersion compensation amount exists in the direction of the dispersion compensation amount where the clock detection value is large. It is done. For this reason, the optimal dispersion compensation amount can be obtained by comparing the clock detection value in the comparison procedure and adjusting the dispersion compensation amount in the direction in which the clock detection value increases. Further, by setting the second candidate value in step (2) close to the first candidate value according to the number of trials, overshooting can be avoided and the chromatic dispersion amount can be estimated at high speed and with high accuracy. be able to.
　従って、本発明は、光ファイバ伝送路における波形歪みを補償する受信装置において、補償すべき波長分散量を高速に、かつ高精度に推定及び設定する波長分散量推定方法を提供することができる。 Therefore, the present invention can provide a chromatic dispersion amount estimation method for estimating and setting a chromatic dispersion amount to be compensated at high speed and with high accuracy in a receiver that compensates for waveform distortion in an optical fiber transmission line.
　本発明に係る波長分散量推定方法は、前記初期値設定手順の前に前記分散補償量の概略値を取得し、前記分散補償量の概略値を前記初期値設定手順における前記分散補償量Ｄ（０）とする概略分散補償量取得手順を有することを特徴とする。 The chromatic dispersion amount estimation method according to the present invention acquires an approximate value of the dispersion compensation amount before the initial value setting procedure, and uses the approximate value of the dispersion compensation amount as the dispersion compensation amount D ( And 0) having an approximate dispersion compensation amount acquisition procedure.
　初段ステップとして、既知信号を用いた波長分散推定法（例えば、特許文献４を参照。）などによって推定された粗推定値を分散補償量の初期値とする。初段ステップの後に、微調整を行うステップを行うことで最適分散補償量の推定を短時間で行うことができる。 As a first step, a rough estimated value estimated by a chromatic dispersion estimation method using a known signal (see, for example, Patent Document 4) is set as an initial value of the dispersion compensation amount. By performing a fine adjustment step after the initial step, the optimum dispersion compensation amount can be estimated in a short time.
　本発明に係る波長分散量推定方法は、前記クロック検出手順、前記プラス側シフト手順及び前記マイナス側シフト手順の少なくとも１つは、異なる時刻に複数回繰り返して平均化することを特徴とする。 The chromatic dispersion amount estimation method according to the present invention is characterized in that at least one of the clock detection procedure, the plus shift procedure, and the minus shift procedure is averaged by repeating a plurality of times at different times.
　クロック検出値を時間平均することで、局所的な変動がある場合でも安定化することができる。 ∙ By averaging the clock detection value over time, it can be stabilized even when there is local fluctuation.
　本発明に係る波長分散量推定方法は、前記プラス側シフト手順及び前記マイナス側シフト手順で前記分散補償量をシフトする前記所定量ΔＤより小さい微少量δＤが設定されており、
　前記クロック検出手順において、前記分散補償量Ｄ（ｋ）におけるクロック検出値Ｓ（ｋ±０）、及び前記分散補償量Ｄ（ｋ）を中心として分散補償量Ｄ（ｋ）±ｎδＤ（ｎは自然数）におけるクロック検出値Ｓ（ｋ±ｎδ）を検出し、
　前記プラス側シフト手順において、前記分散補償量Ｄ（ｋ）＋ΔＤ／Ｍ（ｋ－１）におけるクロック検出値Ｓ（ｋ±０＋）、及び前記分散補償量Ｄ（ｋ）＋ΔＤを中心として分散補償量Ｄ（ｋ）＋ΔＤ／Ｍ（ｋ－１）±ｎδＤ（ｎは自然数）におけるクロック検出値Ｓ（ｋ±ｎδ＋）を検出し、
　前記マイナス側シフト手順において、前記分散補償量Ｄ（ｋ）－ΔＤ／Ｍ（ｋ－１）におけるクロック検出値Ｓ（ｋ±０－）、及び前記分散補償量Ｄ（ｋ）－ΔＤを中心として分散補償量Ｄ（ｋ）－ΔＤ／Ｍ（ｋ－１）±ｎδＤ（ｎは自然数）におけるクロック検出値Ｓ（ｋ±ｎδ－）を検出することを特徴とする。 In the chromatic dispersion amount estimation method according to the present invention, a minute amount δD smaller than the predetermined amount ΔD for shifting the dispersion compensation amount in the plus side shift procedure and the minus side shift procedure is set.
In the clock detection procedure, the clock detection value S (k ± 0) in the dispersion compensation amount D (k) and the dispersion compensation amount D (k) ± nδD (n is a natural number) centering on the dispersion compensation amount D (k) ) To detect the clock detection value S (k ± nδ)
In the plus side shift procedure, the dispersion compensation amount centering on the clock detection value S (k ± 0 +) and the dispersion compensation amount D (k) + ΔD in the dispersion compensation amount D (k) + ΔD / M (k−1) D (k) + ΔD / M (k−1) ± nδD (where n is a natural number) detects a clock detection value S (k ± nδ +),
In the minus side shift procedure, the clock detection value S (k ± 0−) in the dispersion compensation amount D (k) −ΔD / M (k−1) and the dispersion compensation amount D (k) −ΔD are centered. Dispersion compensation amount D (k) −ΔD / M (k−1) ± nδD (where n is a natural number) is detected as a clock detection value S (k ± nδ−).
　分散補償量の周辺でクロック検出値を平均化することで、局所的な変動がある場合でも安定化することができる。 By averaging the clock detection values around the dispersion compensation amount, it is possible to stabilize even if there is a local fluctuation.
　本発明に係る波長分散量推定方法は、クロック検出値Ｓ（ｋ±０）及びクロック検出値Ｓ（ｋ±ｎδ）を平均化して前記クロック検出値Ｓ（ｋ）とし、
　クロック検出値Ｓ（ｋ±０＋）及びクロック検出値Ｓ（ｋ±ｎδ＋）を平均化して前記クロック検出値Ｓ（ｋ＋）とし、
　クロック検出値Ｓ（ｋ±０－）及びクロック検出値Ｓ（ｋ±ｎδ－）を平均化して前記クロック検出値Ｓ（ｋ－）とする
ことを特徴とする。 In the chromatic dispersion amount estimation method according to the present invention, the clock detection value S (k ± 0) and the clock detection value S (k ± nδ) are averaged to obtain the clock detection value S (k),
The clock detection value S (k ± 0 +) and the clock detection value S (k ± nδ +) are averaged to obtain the clock detection value S (k +),
The clock detection value S (k ± 0−) and the clock detection value S (k ± nδ−) are averaged to obtain the clock detection value S (k−).
　分散補償量の周辺でクロック検出値を平均化することで、局所的な変動がある場合でも安定化することができる。 By averaging the clock detection values around the dispersion compensation amount, it is possible to stabilize even if there is a local fluctuation.
　本発明に係る波長分散量推定方法は、前記判定手順で、前記クロック検出値Ｓ（ｋ）と前記クロック検出値Ｓ（ｋ＋）との差及び前記クロック検出値Ｓ（ｋ）と前記クロック検出値Ｓ（ｋ－）との差が所定の閾値未満の場合、前記分散補償量Ｄ（ｋ）を最適分散補償量として決定して前記分散補償量の推定を完了することを特徴とする。 In the chromatic dispersion amount estimation method according to the present invention, in the determination procedure, the difference between the clock detection value S (k) and the clock detection value S (k +) and the clock detection value S (k) and the clock detection value are determined. When the difference from S (k−) is less than a predetermined threshold, the dispersion compensation amount D (k) is determined as the optimum dispersion compensation amount, and the estimation of the dispersion compensation amount is completed.
　クロック検出値の差が小さく、最適値がどちらの方向にあるか不確定な状態で推定を行うことを避けることで、推定動作を安定化することができる。 The estimation operation can be stabilized by avoiding estimation in a state where the difference between the clock detection values is small and the optimum value is in an uncertain state.
　本発明に係る波長分散補償回路は、前記光ファイバ伝送路から受信した光アナログ波形をデジタル信号に変換するアナログデジタル変換器と、
　前記アナログデジタル変換器が出力する前記デジタル信号が持つ前記光ファイバ伝送路の波長分散による波形歪みを、前記波長分散量推定方法で推定した前記分散補償量で補償するデジタル信号処理器と、
　前記アナログデジタル変換器が出力する前記デジタル信号に含まれる受信データのシンボル到来タイミングクロックを抽出し、前記シンボル到来タイミングクロックの強度を前記クロック検出値として出力するシンボルクロック抽出器と、
を備える。 The chromatic dispersion compensation circuit according to the present invention is an analog-digital converter that converts an optical analog waveform received from the optical fiber transmission line into a digital signal;
A digital signal processor that compensates for waveform distortion due to chromatic dispersion of the optical fiber transmission line of the digital signal output by the analog-digital converter with the dispersion compensation amount estimated by the chromatic dispersion amount estimation method;
A symbol clock extractor that extracts a symbol arrival timing clock of received data included in the digital signal output by the analog-digital converter and outputs the intensity of the symbol arrival timing clock as the clock detection value;
Is provided.
　本発明に係る波長分散補償回路は、前記波長分散量推定方法を採用する。従って、本発明は、光ファイバ伝送路における波形歪みを補償する受信装置において、補償すべき波長分散量を高速に、かつ高精度に推定及び設定する波長分散補償回路を提供することができる。 The chromatic dispersion compensation circuit according to the present invention employs the chromatic dispersion amount estimation method. Therefore, the present invention can provide a chromatic dispersion compensation circuit that estimates and sets the amount of chromatic dispersion to be compensated at high speed and with high accuracy in a receiver that compensates for waveform distortion in an optical fiber transmission line.
　本発明に係る受信装置は、前記波長分散補償回路を含む。 The receiving apparatus according to the present invention includes the chromatic dispersion compensation circuit.
　本発明に係る受信装置は、前記波長分散補償回路を備える。従って、本発明は、光ファイバ伝送路における波形歪みを補償する受信装置において、補償すべき波長分散量を高速に、かつ高精度に推定及び設定する受信装置を提供することができる。 A receiving apparatus according to the present invention includes the chromatic dispersion compensation circuit. Therefore, the present invention can provide a receiving apparatus that compensates for waveform distortion in an optical fiber transmission line and estimates and sets the amount of chromatic dispersion to be compensated at high speed and with high accuracy.
　本発明は、光ファイバ伝送路における波形歪みを補償する受信装置において、補償すべき波長分散量を高速に、かつ高精度に推定及び設定する波長分散量推定方法、波長分散補償回路、及び受信装置を提供することができる。 The present invention relates to a chromatic dispersion amount estimating method, a chromatic dispersion compensation circuit, and a receiving apparatus for estimating and setting a chromatic dispersion amount to be compensated at high speed and with high accuracy in a receiving apparatus for compensating waveform distortion in an optical fiber transmission line. Can be provided.
本発明に係る波長分散量推定方法を説明する図である。It is a figure explaining the chromatic dispersion amount estimation method which concerns on this invention. 本発明に係る波長分散量推定方法を説明するフロー図である。It is a flowchart explaining the chromatic dispersion amount estimation method which concerns on this invention. 本発明に係る波長分散量推定方法を説明する図である。It is a figure explaining the chromatic dispersion amount estimation method which concerns on this invention. 本発明に係る波長分散量推定方法を説明するフロー図である。It is a flowchart explaining the chromatic dispersion amount estimation method which concerns on this invention. 本発明に係る受信装置を説明する図である。It is a figure explaining the receiver which concerns on this invention.
　添付の図面を参照して本発明の実施形態を説明する。以下に説明する実施形態は本発明の実施例であり、本発明は、以下の実施形態に制限されるものではない。なお、本明細書及び図面において符号が同じ構成要素は、相互に同一のものを示すものとする。 Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.
　図５は、本実施形態の受信装置３００を説明する図である。受信装置３００は波長分散補償回路１０１を含む。波長分散補償回路１０１は、光ファイバ伝送路から受信した光アナログ波形をデジタル信号に変換するアナログデジタル変換器１１と、アナログデジタル変換器１１が出力するデジタル信号が持つ光ファイバ伝送路の波長分散による波形歪みを、以下で説明する波長分散量推定方法で推定した分散補償量で補償するデジタル信号処理器１２と、アナログデジタル変換器１１が出力するデジタル信号に含まれる受信データのシンボル到来タイミングクロックを抽出し、シンボル到来タイミングクロックの強度をクロック検出値として出力するシンボルクロック抽出器１３と、を備える。 FIG. 5 is a diagram illustrating the receiving device 300 according to the present embodiment. The receiving apparatus 300 includes a chromatic dispersion compensation circuit 101. The chromatic dispersion compensation circuit 101 is based on an analog-digital converter 11 that converts an optical analog waveform received from an optical fiber transmission path into a digital signal, and wavelength dispersion of the optical fiber transmission path that the digital signal output from the analog-digital converter 11 has. A digital signal processor 12 that compensates for waveform distortion with a dispersion compensation amount estimated by a chromatic dispersion amount estimation method described below, and a symbol arrival timing clock of received data included in the digital signal output from the analog-digital converter 11 And a symbol clock extractor 13 for extracting and outputting the intensity of the symbol arrival timing clock as a clock detection value.
　デジタル信号処理器１２が行う波長分散量推定方法の実施形態を説明する。 An embodiment of a chromatic dispersion amount estimation method performed by the digital signal processor 12 will be described.
（実施形態１）
　まず、粗調整プロセスとして、既知信号を用いた波長分散推定法などによって推定された粗推定値を初期値として分散補償回路に設定する。このとき、波長分散の大部分が補償され、推定誤差などによって生じる残留分散による波形歪みを受けた波形が分散補償回路から出力される。 (Embodiment 1)
First, as a rough adjustment process, a rough estimation value estimated by a chromatic dispersion estimation method using a known signal or the like is set as an initial value in the dispersion compensation circuit. At this time, most of the chromatic dispersion is compensated, and a waveform subjected to waveform distortion due to residual dispersion caused by an estimation error or the like is output from the dispersion compensation circuit.
　この後、微調整プロセスに入る。図１及び図２は、本実施形態の微調整プロセスを説明する図である。Ｄ（ｋ）はデジタル信号処理器１２に設定する分散補償量を示す。まず、第一段階として、初期値ｋ＝０の分散補償量Ｄ（０）を設定し、クロック同期の検出信号値を測定してメモリに記憶する。これをクロック検出値Ｓ（０）とする。次に、図１（ａ）にあるように、第一段階として、
［１］分散補償量Ｄ（０）からある一定のシフト量ΔＤだけ正の方向にシフトさせる（分散補償量Ｄ（０）＋Δ）。そして、クロック同期のクロック検出値Ｓ（０＋）を測定して記憶する。
［２］同様に、分散補償量Ｄ（０）からある一定のシフト量ΔＤだけ負の方向にシフトさせ（分散補償量Ｄ（０）－Δ）、その際のクロック同期のクロック検出値Ｓ（０－）を測定して格納する。
　一定のシフト量ΔＤは、初期値が有する期待値からのずれ量の最大値程度とする。ここで、初期値は用いる粗推定アルゴリズム（例えば、特許文献４のアルゴリズム）に依存する。例えば、特許文献４で補償範囲として例示する分散量２００００ｐｓｅｃ／ｎｍの１．５～５％の誤差と仮定して、ΔＤを３００～１０００ｐｓｅｃ／ｎｍとする。 After this, the fine adjustment process is started. 1 and 2 are diagrams for explaining the fine adjustment process of the present embodiment. D (k) represents the dispersion compensation amount set in the digital signal processor 12. First, as a first step, a dispersion compensation amount D (0) with an initial value k = 0 is set, and a clock synchronization detection signal value is measured and stored in a memory. This is defined as a clock detection value S (0). Next, as shown in FIG.
[1] Shift from the dispersion compensation amount D (0) in a positive direction by a certain shift amount ΔD (dispersion compensation amount D (0) + Δ). Then, the clock-synchronized clock detection value S (0+) is measured and stored.
[2] Similarly, the dispersion compensation amount D (0) is shifted in a negative direction by a certain shift amount ΔD (dispersion compensation amount D (0) −Δ), and the clock detection value S ( Measure and store 0-).
The constant shift amount ΔD is about the maximum value of the deviation amount from the expected value of the initial value. Here, the initial value depends on the rough estimation algorithm to be used (for example, the algorithm of Patent Document 4). For example, assuming that the error is 1.5 to 5% of the dispersion amount 20000 psec / nm exemplified as the compensation range in Patent Document 4, ΔD is set to 300 to 1000 psec / nm.
　クロック検出値が大きい符号方向に最適値が存在すると考えられる。このため、Ｓ（０），Ｓ（０＋），Ｓ（０－）を比較する。クロック検出値がＳ（０＋）＞Ｓ（０－）の場合、Ｄ（０）＋ΔＤを次の分散補償量Ｄ（１）に設定する。逆に、クロック検出値がＳ（０＋）＜Ｓ（０－）の場合、Ｄ（０）－ΔＤを次の分散補償量Ｄ（１）に設定する。Ｓ（０＋），Ｓ（０－）ともにＳ（０）より小さい場合、すなわち、Ｓ（０）＞Ｓ（０＋）かつＳ（０）＞Ｓ（０－）の場合、分散補償量Ｄ（１）＝Ｄ（０）とする。 It is considered that the optimum value exists in the code direction where the clock detection value is large. Therefore, S (0), S (0+), and S (0−) are compared. When the clock detection value is S (0 +)> S (0−), D (0) + ΔD is set to the next dispersion compensation amount D (1). Conversely, when the clock detection value is S (0 +) <S (0−), D (0) −ΔD is set to the next dispersion compensation amount D (1). When both S (0+) and S (0−) are smaller than S (0), that is, when S (0)> S (0+) and S (0)> S (0−), the dispersion compensation amount D (1 ) = D (0).
　ここでは、Ｓ（０＋）＞Ｓ（０－）であった場合を想定し、分散補償量Ｄ（１）＝Ｄ（０）＋ΔＤに設定したとして、以降のプロセスを説明する。 Here, assuming that S (0 +)> S (0−), the following process will be described assuming that the dispersion compensation amount D (1) = D (0) + ΔD.
　図１（ｂ）の第二段階として、分散補償量Ｄ（１）＝Ｄ（０）＋ΔＤを中心として、正負の方向にシフト量ΔＤ／２だけシフトさせる［３］［４］。分散補償量をそれぞれＤ（１）＋ΔＤ／２、Ｄ（１）－ΔＤ／２に設定した場合のクロック検出値Ｓ（１＋）、Ｓ（１－）を検出し、メモリに格納する。そして、両者を比較して、Ｓ（１＋）＞Ｓ（１－）の場合には、補償分散量をＤ（２）＝Ｄ（１）＋ΔＤ／２に、Ｓ（１＋）＜Ｓ（１－）の場合には、Ｄ（２）＝Ｄ（１）－ΔＤ／２に設定する。また、Ｓ（１＋），Ｓ（１－）ともにＳ（１）より小さい場合、Ｓ（１）＞　Ｓ（１＋）かつＳ（１）＞Ｓ（１－）も考えられ、この場合はＤ（２）＝Ｄ（１）とする。ここでは、Ｓ（１＋）＜Ｓ（１－）であった場合を想定し、補償分散量をＤ（２）＝Ｄ（１）－ΔＤ／２に設定したとして、以降を説明する。 As the second stage in FIG. 1B, the shift amount is shifted in the positive and negative directions by a shift amount ΔD / 2 around the dispersion compensation amount D (1) = D (0) + ΔD [3] [4]. Clock detection values S (1+) and S (1−) when the dispersion compensation amounts are set to D (1) + ΔD / 2 and D (1) −ΔD / 2 are detected and stored in the memory. Then, comparing the two, if S (1 +)> S (1-), the compensation dispersion amount is D (2) = D (1) + ΔD / 2, and S (1 +) <S (1− ), D (2) = D (1) −ΔD / 2 is set. If S (1+) and S (1-) are smaller than S (1), S (1)> S (1+) and S (1)> S (1-) are also considered. In this case, D ( 2) = D (1). Here, assuming that S (1 +) <S (1-), the following explanation will be made assuming that the compensation dispersion amount is set to D (2) = D (1) −ΔD / 2.
　第三段階としては、補償分散量Ｄ（２）を中心として、正負方向にシフト量ΔＤ／４だけシフトさせる［５］［６］。分散補償量を正負にシフトさせたときのそれぞれのクロック同期の検出信号Ｓ（２＋）、Ｓ（２－）を検出してメモリに記憶する。そして、両者を比較してより大きい符号方向にシフトさせる。以降同様のプロセスを繰り返すことで、最適な補償分散量に漸近させることができる。ここで第ｋ段階における補償分散量Ｄ（ｋ）のシフト量は、ΔＤ／（２（ｋ－１））となっており、プロセスが進む毎に半減する。
　このように、シフト量をΔＤ／２，ΔＤ／４，ΔＤ／８，・・・と半減させてプロセスを繰り返すが、その反復回数は最終的な目標誤差範囲より、シフト量が小さくなるまでは繰り返す必要がある。例えば、ΔＤ＝１０２４ｐｓｅｃ／ｎｍ、目標誤差５０ｐｓｅｃ／ｎｍとすると、シフト量はプロセス毎に１０２４、５１２、２５６、１２６、６４、３２、１６（ｐｓｅｃ／ｎｍ）のように推移する。このため、シフト量が目標誤差より小さくなる６、７回程度、プロセスを繰り返す必要がある。時間に余裕があれば、シフト量がさらに小さくなるまでプロセスを繰り返してもよい。 As a third stage, the shift amount ΔD / 4 is shifted in the positive and negative directions around the compensation dispersion amount D (2) [5] [6]. The respective clock synchronization detection signals S (2+) and S (2-) when the dispersion compensation amount is shifted to positive and negative are detected and stored in the memory. Then, both are compared and shifted in a larger code direction. Thereafter, by repeating the same process, the optimum compensation dispersion amount can be made asymptotic. Here, the shift amount of the compensation dispersion amount D (k) at the k-th stage is ΔD / (2 (k−1) ), and is halved each time the process proceeds.
In this way, the process is repeated with the shift amount halved to ΔD / 2, ΔD / 4, ΔD / 8,..., But the number of iterations is until the shift amount becomes smaller than the final target error range. Need to repeat. For example, when ΔD = 1024 psec / nm and the target error is 50 psec / nm, the shift amount changes as 1024, 512, 256, 126, 64, 32, 16 (psec / nm) for each process. For this reason, it is necessary to repeat the process about 6 to 7 times when the shift amount becomes smaller than the target error. If there is enough time, the process may be repeated until the shift amount is further reduced.
　ここで、本来検出信号には誤差が含まれるため、Ｓ（ｋ＋），Ｓ（ｋ－），及びＳ（ｋ）の差分が設定した閾値より小さい場合には、再度Ｓ（ｋ）を設定し、やり直し測定する選択がある。これにより、差分が小さく、最適値が正負どちらの方向に存在するか不確定な状況で、不確定な情報を元にシフトさせることは不安定な動作を引き起こす危険性を低減することができる。なお、上記例では補償分散量Ｄ（ｋ）のシフト量を段階毎に半減する例、すなわちΔＤ／（２（ｋ－１））を説明したが、シフト量はΔＤ／（Ｍ（ｋ－１））であってもよい（Ｍは１以上の実数）。 Here, since the detection signal originally includes an error, if the difference between S (k +), S (k−), and S (k) is smaller than the set threshold value, S (k) is set again. There is an option to measure again. As a result, in a situation where the difference is small and it is uncertain whether the optimum value is positive or negative, shifting based on uncertain information can reduce the risk of causing an unstable operation. In the above example, the shift amount of the compensation dispersion amount D (k) is halved for each step, that is, ΔD / (2 (k−1) ), but the shift amount is ΔD / (M (k−1) ) ) (M is a real number of 1 or more).
　上記の手法では、各設定値におけるクロック検出信号の１回の測定値によって、分散補償量の設定値を決定していくプロセスになっている。従って、それぞれの測定におけるＳ（ｋ）の誤差が大きい場合には、最適化のシーケンスが不安定な動作となってしまう可能性がある。安定化するための手法として、各設定値に対して異なる時刻において複数回測定して、その平均値を比較することで正負符号のどちらの方向にシフトすべきかを判断することで、動作の安定化が期待される。 In the above method, the dispersion compensation amount setting value is determined based on one measurement value of the clock detection signal at each setting value. Therefore, when the error of S (k) in each measurement is large, the optimization sequence may be unstable. As a method for stabilization, measure multiple times at different times for each set value, and compare the average value to determine which direction of positive or negative sign should be used for stable operation. Is expected.
　上記の例では、分散補償量の初期値として、分散推定回路の粗推定値を利用したが、外部から与えられた分散値を設定する場合もある。このような例として、伝送路の分散量を予め分散測定器などで測定した場合などが考えられる。 In the above example, the coarse estimation value of the dispersion estimation circuit is used as the initial value of the dispersion compensation amount. However, a dispersion value given from the outside may be set. As such an example, a case where the dispersion amount of the transmission line is previously measured with a dispersion measuring device or the like can be considered.
（実施形態２）
　クロック同期回路の検出信号の残留分散依存性が局所的に揺らぐ可能性がある。この場合、第一の実施例では、局所的な変化のために正方向にシフトすべきか、負方向にシフトすべきかの判断が困難となる場合がある。本実施形態は、局所的な残留分散依存性がある状況であっても、平均化することで高精度に分散補償量のシフト方向を判定し、安定的に分散補償量の推定を行うことができる。 (Embodiment 2)
There is a possibility that the residual dispersion dependency of the detection signal of the clock synchronization circuit fluctuates locally. In this case, in the first embodiment, it may be difficult to determine whether to shift in the positive direction or in the negative direction due to local changes. In this embodiment, even in a situation where there is local residual dispersion dependency, averaging can be performed to determine the shift direction of the dispersion compensation amount with high accuracy and stably estimate the dispersion compensation amount. it can.
　図３は、本実施形態の微調整プロセスを説明する図である。初期ステップとして、既知信号を用いた波長分散推定法などによって推定された粗推定の分散補償量Ｄ（０）を初期値として分散補償回路に設定する。このとき、波長分散の大部分が補償され、推定誤差などによって生じる残留分散による波形歪みを受けた波形が分散補償回路から出力される。 FIG. 3 is a diagram for explaining the fine adjustment process of the present embodiment. As an initial step, a coarse compensation dispersion compensation amount D (0) estimated by a chromatic dispersion estimation method using a known signal or the like is set as an initial value in the dispersion compensation circuit. At this time, most of the chromatic dispersion is compensated, and a waveform subjected to waveform distortion due to residual dispersion caused by an estimation error or the like is output from the dispersion compensation circuit.
　初期ステップでは、初期設定の分散補償量Ｄ（０）におけるクロック同期のクロック検出値Ｓ（０）を測定し、記憶する。次に、第一段階として図３（ａ）に示すように、Ｄ（０）からある微小量δＤだけ、分散補償設定値を正の方向にシフトさせる。そして、クロック同期のクロック検出値Ｓ（０＋δ）を測定し、記憶する。さらに、δＤづつ正方向にシフトさせていき、２δＤ、３δＤ、・・・のポイントにおいて、クロック同期のクロック検出値Ｓ（０＋２δ）、Ｓ（０＋３δ）、・・・、Ｓ（０＋ｎδ）を測定、メモリに格納してもよい。また、負の方向に微少量δＤだけシフトさせ、その際のクロック同期のクロック検出値Ｓ（０－δ）を測定し、メモリに格納する。同様に、δＤづつ負方向にシフトさせていき、－２δＤ、－３δＤ、・・・のポイントにおいて、クロック同期のクロック検出値Ｓ（０－２δ）、Ｓ（０－３δ）、・・・、Ｓ（０－ｎδ）を測定、メモリに格納してもよい。この部分の制御ブロック図を図４に示す。これをＮ回だけ繰り返す。ここでは、正負に対して、均等なポイント数を測定する例を示したが、特に正負均等である必要もない。例えば、Ｄ（０）、及びＤ（０）＋δＤのみ測定してもよい。
　微少量δＤは、図３の分散補償量に対するクロック検出値Ｓ（ｋ）に発生するリップルの周期及び振幅に基づいて設定する。具体的には、微少量δＤはリップルの周期以下とすればよい。例えば、リップルの振幅がクロック検出値Ｓ（ｋ）の１０％程度である場合、設定分散補償量Ｄ（ｋ）をδＤシフトした際のクロック検出値Ｓ（ｋ）の平均的な変動量はクロック検出値Ｓ（ｋ）の１０％未満とする。
　また、リップルの周期が条件によって変化する場合、微少量δＤは最終的な目標誤差の標準偏差より十分小さくする。例えば、δＤは目標誤差の１／３～１／５０、好ましくは１／５～１／２０、より好ましくは１／７～１／２０とすることができる。具体的数値として、最終的な目標誤差が５０ｐｓｅｃ／ｎｍ～１５０ｐｓｅｃ／ｎｍであれば、δＤは１ｐｓｅｃ／ｎｍ～５０ｐｓｅｃ／ｎｍ程度、好ましくは４ｐｓｅｃ／ｎｍ～３０ｐｓｅｃ／ｎｍ程度に設定する。また、δＤをｋに従って変化させる場合、ΔＤと同様にδＤ／（２（ｋ－１））と変化させる。この場合、δＤをΔＤの１／３～１／５０、好ましくは１／５～１／１０、より好ましくは１／５～１／７とすることができる。 In the initial step, the clock-synchronized clock detection value S (0) at the initially set dispersion compensation amount D (0) is measured and stored. Next, as shown in FIG. 3A, the dispersion compensation set value is shifted in the positive direction by a small amount δD from D (0) as the first step. Then, the clock detection value S (0 + δ) synchronized with the clock is measured and stored. Further, shifting in the positive direction by δD, and measuring clock-synchronized clock detection values S (0 + 2δ), S (0 + 3δ),..., S (0 + nδ) at the points 2δD, 3δD,. It may be stored in a memory. Further, a small amount δD is shifted in the negative direction, and the clock detection value S (0−δ) of the clock synchronization at that time is measured and stored in the memory. Similarly, it is shifted in the negative direction by δD, and at the points −2δD, −3δD,..., The clock detection values S (0-2δ), S (0-3δ),. S (0−nδ) may be measured and stored in the memory. A control block diagram of this part is shown in FIG. Repeat this N times. Here, an example in which the number of equal points is measured with respect to positive and negative is shown, but it is not necessary to be particularly equal to positive and negative. For example, only D (0) and D (0) + δD may be measured.
The minute amount δD is set based on the period and amplitude of the ripple generated in the clock detection value S (k) with respect to the dispersion compensation amount in FIG. Specifically, the minute amount δD may be set to be equal to or less than the ripple period. For example, when the amplitude of the ripple is about 10% of the clock detection value S (k), the average fluctuation amount of the clock detection value S (k) when the set dispersion compensation amount D (k) is shifted by δD is the clock. It is less than 10% of the detected value S (k).
When the ripple period changes depending on conditions, the minute amount δD is made sufficiently smaller than the standard deviation of the final target error. For example, δD can be set to 1/3 to 1/50 of the target error, preferably 1/5 to 1/20, and more preferably 1/7 to 1/20. As a specific numerical value, if the final target error is 50 psec / nm to 150 psec / nm, δD is set to about 1 psec / nm to 50 psec / nm, preferably about 4 psec / nm to 30 psec / nm. Further, when δD is changed according to k, it is changed to δD / (2 (k−1) ) similarly to ΔD. In this case, δD can be set to 1/3 to 1/50 of ΔD, preferably 1/5 to 1/10, and more preferably 1/5 to 1/7.
　次に、Ｄ（０）を中心として、シフト量ΔＤだけ正方向にシフトさせ、Ｓ（０＋）を検出し、メモリに格納する［１］。さらに、そこからδＤだけ順々に正方向及び負方向にシフトさせて、シンボルクロック抽出回路のクロック検出値Ｓ（０±ｎδ＋）を検出し、メモリに格納する。同様に、Ｄ（０）を中心として、シフト量ΔＤだけ負方向にシフトさせて、Ｓ（０－）及びＳ（０±ｎδ－）を検出し、メモリに格納する［２］。ここで、一般には、ΔＤ＞δＤである。 Next, shifting in the positive direction by the shift amount ΔD with D (0) as the center, S (0+) is detected and stored in the memory [1]. Further, the signal is shifted in the positive and negative directions sequentially by δD to detect the clock detection value S (0 ± nδ +) of the symbol clock extraction circuit and store it in the memory. Similarly, shifting in the negative direction by the shift amount ΔD with D (0) as the center, S (0−) and S (0 ± nδ−) are detected and stored in the memory [2]. Here, in general, ΔD> δD.
　次に、それぞれ分散補償値Ｄ（０），Ｄ（０）＋ΔＤ、Ｄ（０）－ΔＤを中心に正負方向に微小量シフトしたときのクロック検出値Ｓ（０±ｎδ），Ｓ（０±ｎδ＋），Ｓ（０±ｎδ－）を比較して、クロック同期の検出信号が大きくなる符号方向を総合的に判断して、分散補償値をシフトさせる。総合的に判断する一例としては、Ｓ（０±ｎδ），Ｓ（０±ｎδ＋），Ｓ（０±ｎδ－）それぞれをｎに対して平均化処理を施し、それぞれの平均値Ｓａｖｇ（０），Ｓａｖｇ（０＋），Ｓａｖｇ（０－）を算出する。例えば、Ｓａｖｇ（０＋）の算出例を式で記述すると、次式のようになる。
Figure JPOXMLDOC01-appb-M000001
 　Ｎも精度と時間とのバランスを考慮して設定する。ただし、δＤが固定の場合、ΔＤとδＤの関係で制限される。δＤ＞ΔＤ／（２（Ｎ－１））となると、誤差を低減できないので、この条件を満たすＮとする。例えば、Ｎは３以上７以下に設定する。 Next, the clock detection values S (0 ± nδ) and S (0 ± 0) when the dispersion compensation values D (0), D (0) + ΔD, and D (0) −ΔD are shifted by a small amount in the positive and negative directions, respectively. n.delta. +) and S (0. ± .n.delta.-) are compared to comprehensively determine the sign direction in which the clock synchronization detection signal becomes large, and the dispersion compensation value is shifted. As an example of comprehensive determination, S (0 ± nδ), S (0 ± nδ +), and S (0 ± nδ−) are averaged with respect to n, and each average value Savg (0) , Savg (0+), Savg (0−) are calculated. For example, when a calculation example of Savg (0+) is described by an equation, the following equation is obtained.
Figure JPOXMLDOC01-appb-M000001
 N is also set in consideration of the balance between accuracy and time. However, when δD is fixed, it is limited by the relationship between ΔD and δD. If δD> ΔD / (2 (N−1) ), the error cannot be reduced. For example, N is set to 3 or more and 7 or less.
　検出信号平均値がＳａｖｇ（０＋）＞Ｓａｖｇ（０－）の場合には、分散補償量Ｄ（１）をＤ（０）＋ΔＤに設定する。逆に、検出値がＳａｖｇ（０＋）＜Ｓａｖｇ（０－）の場合には、分散補償量Ｄ（１）をＤ（０）－ΔＤに設定する。また、Ｓａｖｇ（０＋），Ｓａｖｇ（０－）ともにＳａｖｇ（０）より小さい場合、Ｓａｖｇ（０）＞Ｓａｖｇ（０＋）かつＳａｖｇ（０）＞Ｓａｖｇ（０－）となる場合も考えられ、この場合はＤ（１）＝Ｄ（０）とする。ここでは、Ｓａｖｇ（０＋）＞Ｓａｖｇ（０－）であった場合を想定し、Ｄ（１）＝Ｄ（０）＋ΔＤに設定したとして、以降のプロセスを説明する。 When the average detection signal value is Savg (0 +)> Savg (0−), the dispersion compensation amount D (1) is set to D (0) + ΔD. Conversely, when the detected value is Savg (0 +) <Savg (0−), the dispersion compensation amount D (1) is set to D (0) −ΔD. Further, when both Savg (0+) and Savg (0−) are smaller than Savg (0), it may be considered that Savg (0)> Savg (0+) and Savg (0)> Savg (0−). Is D (1) = D (0). Here, assuming the case of Savg (0 +)> Savg (0−), assuming that D (1) = D (0) + ΔD is set, the subsequent process will be described.
　第二段階以降の制御方法は、実施形態１と同様に、分散補償量Ｄ（１）の点、Ｄ（１）＋ΔＤ／２の点、Ｄ（１）－ΔＤ／２の点におけるクロック検出値を比較して、正負シフト方向を判定する。さらに、正負のシフト方向判断の信頼度を向上するため、第一段階で説明したように、それぞれのポイント付近で正負方向にδＤづつシフトさせ、それらの平均化したクロック検出値を用いて正負シフト方向を判断する。 As in the first embodiment, the control method after the second stage is the clock detection value at the point of dispersion compensation amount D (1), the point of D (1) + ΔD / 2, and the point of D (1) −ΔD / 2. Are compared to determine the positive / negative shift direction. Furthermore, in order to improve the reliability of the positive / negative shift direction determination, as described in the first stage, the positive / negative shift is performed using δD shifted in the positive / negative direction near each point and using the averaged clock detection values. Determine the direction.
　まず、Ｄ（１）＝Ｄ（０）＋ΔＤを中心として、正負の方向にｎ×δＤだけシフトさせ、Ｓ（１±ｎδＤ）のクロック検出値を取得する［３］［４］。さらに、それらの検出値を用いて、平均化処理を施したＳａｖｇ（１）を求める。 First, it is shifted by n × δD in the positive and negative directions around D (1) = D (0) + ΔD, and the clock detection value of S (1 ± nδD) is acquired [3] [4]. Furthermore, Savg (1) subjected to the averaging process is obtained using those detected values.
　次に、分散補償量を正の方向にシフト量ΔＤ／２だけシフトさせ［１］、分散補償量Ｄ（１）＋ΔＤ／２を中心として正負方向に微小量ｎ×δＤづつシフトさせ、クロック検出値Ｓ（１±ｎδ＋）を取得する［７］［８］。さらに、それらの検出値を用いて、平均化処理を施したＳａｖｇ（１＋）を求める。同様に、分散補償量を負の方向にシフト量ΔＤ／２だけシフトさせ［２］、分散補償量Ｄ（１）－ΔＤ／２を中心として、正負方向に微小量ｎ×δＤづつシフトさせ、クロック検出値Ｓ（１±ｎδ－）を取得する。さらに、それらの検出値を用いて、平均化処理を施したＳａｖｇ（１－）を求める。 Next, the dispersion compensation amount is shifted in the positive direction by the shift amount ΔD / 2 [1], and the dispersion compensation amount D (1) + ΔD / 2 is shifted in the positive and negative directions by a small amount n × δD to detect the clock. The value S (1 ± nδ +) is acquired [7] [8]. Further, using the detected values, Savg (1+) subjected to the averaging process is obtained. Similarly, the dispersion compensation amount is shifted by a shift amount ΔD / 2 in the negative direction [2], and the dispersion compensation amount D (1) −ΔD / 2 is shifted by a minute amount n × δD in the positive and negative directions around the center. The clock detection value S (1 ± nδ−) is acquired. Further, using the detected values, Savg (1-) subjected to the averaging process is obtained.
　さらに、これらＳａｖｇ（１）、Ｓａｖｇ（１＋）、Ｓａｖｇ（１－）を比較して、より検出信号が大きくなる補償分散の正負シフト方向を判断する。Ｓａｖｇ（１＋）＞Ｓａｖｇ（１－）の場合には、補償分散量をＤ（２）＝Ｄ（１）＋ΔＤ／２に設定する。Ｓａｖｇ（１＋）＜Ｓａｖｇ（１－）の場合には、Ｄ（２）＝Ｄ（１）－ΔＤ／２に設定する。また、Ｓａｖｇ（１＋），Ｓａｖｇ（１－）ともにＳ（１）より小さい場合、Ｓａｖｇ（１）＞　Ｓａｖｇ（１＋）かつＳａｖｇ（１）＞Ｓａｖｇ（１－）も考えられる。この場合はＤ（２）＝Ｄ（１）とする。なお、Ｓａｖｇ（１）、Ｓａｖｇ（１＋）、Ｓａｖｇ（１－）の差が誤差未満など所定値以下の場合には、Ｄ２＝Ｄ１としてもよい。 Further, these Savg (1), Savg (1+), and Savg (1-) are compared, and the positive / negative shift direction of the compensation dispersion in which the detection signal becomes larger is determined. When Savg (1 +)> Savg (1-), the compensation dispersion amount is set to D (2) = D (1) + ΔD / 2. If Savg (1 +) <Savg (1-), D (2) = D (1) −ΔD / 2 is set. When both Savg (1+) and Savg (1-) are smaller than S (1), Savg (1)> Savg (1+) and Savg (1)> Savg (1-) are also conceivable. In this case, D (2) = D (1). If the difference between Savg (1), Savg (1+), and Savg (1-) is less than a predetermined value such as less than an error, D2 = D1 may be set.
　ここでは、Ｓａｖｇ（１＋）＜Ｓａｖｇ（１－）であった場合を想定し、補償分散量をＤ（２）＝Ｄ（１）－ΔＤ／２に設定したとして以降を説明する。 Here, assuming that Savg (1 +) <Savg (1-), the following description will be made assuming that the compensation dispersion amount is set to D (2) = D (1) −ΔD / 2.
　第三段階も上記説明と同様に補償分散量の正負シフト方向を判断する。補償分散量がＤ（２）のポイント、Ｄ（２）を中心として正負方向にシフト量ΔＤ／４だけシフトさせたポイント、これら３点のポイント
Ｄ（２）
Ｄ（２）＋ΔＤ／４
Ｄ（２）－ΔＤ／４
でのクロック検出値の比較を実施する。第三段階では、シフト量がΔＤ／４と更に半減している。それら３ポイントにおいて、正負方向に微小量ｎ×±δＤづつシフト点のクロック検出値
Ｓ（１±ｎδ）
Ｓ（１±ｎδ＋）
Ｓ（１±ｎδ－）
を取得する。さらに、これらの平均値
Ｓａｖｅ（２）
Ｓａｖｇ（２＋）
Ｓａｖｇ（２－）
を求め、第二段階で説明したように次の段階のシフト方向を判断する。 In the third stage, the positive / negative shift direction of the compensation dispersion amount is determined in the same manner as described above. A point where the compensation dispersion amount is D (2), a point shifted by a shift amount ΔD / 4 in the positive and negative directions around D (2), and these three points D (2)
D (2) + ΔD / 4
D (2) -ΔD / 4
Comparison of the clock detection value at. In the third stage, the shift amount is further halved to ΔD / 4. At these three points, the clock detection value S (1 ± nδ) at the shift point by a minute amount n × ± δD in the positive and negative directions.
S (1 ± nδ +)
S (1 ± nδ-)
To get. Further, the average value Save (2) of these
Savg (2+)
Savg (2-)
As described in the second step, the shift direction of the next step is determined.
　以降同様のプロセスを繰り返すことで、最適な補償分散量に漸近させることができる。ここで第ｋ段階のシフト量は、ΔＤ／（２（ｋ－１））となっており、プロセスが進む毎に半減していく。なお、上記例では補償分散量Ｄ（ｋ）のシフト量を段階毎に半減する例、すなわちΔＤ／（２（ｋ－１））を説明したが、実施形態１と同用にシフト量はΔＤ／（Ｍ（ｋ－１））であってもよい。 Thereafter, by repeating the same process, the optimum compensation dispersion amount can be made asymptotic. Here, the shift amount at the k-th stage is ΔD / (2 (k−1) ), which is halved as the process proceeds. In the above example, the example in which the shift amount of the compensation dispersion amount D (k) is reduced by half, that is, ΔD / (2 (k−1) ) has been described. However, the shift amount is ΔD as in the first embodiment. / (M (k-1) ).
　上記の説明では、各段階でシフト量ΔＤ、ΔＤ／２、ΔＤ／４、・・・と半減するにも関わらず、平均化処理するための微小量はδＤの一定値である例を示した。この例では、δＤより細かい単位での分散補償量の最適化ができない。そこで、各段階でシフト量がΔＤ、ΔＤ／２、ΔＤ／４、・・・と半減するに伴い、微小量δＤも、平均化が有効な範囲で小さくしてもよい。例えば、微小量をδＤ、δＤ／２、δＤ／４、・・・と小さく変化させてもよい。 In the above description, although the shift amounts ΔD, ΔD / 2, ΔD / 4,... Are halved at each stage, the minute amount for the averaging process is a constant value of δD. . In this example, the dispersion compensation amount cannot be optimized in units smaller than δD. Therefore, as the shift amount is halved to ΔD, ΔD / 2, ΔD / 4,... At each stage, the minute amount δD may be reduced within a range where the averaging is effective. For example, the minute amount may be changed as small as δD, δD / 2, δD / 4,.
　以上説明した様に，本発明によれば，光通信システムの波長分散補償回路の補償量に対して微小な変化を与え、クロック検出信号をモニタ信号として最適な補償量を探索する際に、与える変化量を試行回数の度に半減させていくことで効率的に最適な分散補償量を検出することができる。 As described above, according to the present invention, a minute change is given to the compensation amount of the chromatic dispersion compensation circuit of the optical communication system, and this is given when searching for the optimum compensation amount using the clock detection signal as a monitor signal. The optimum dispersion compensation amount can be efficiently detected by reducing the change amount by half for each trial.
１１：アナログデジタル変換器
１２：デジタル信号処理器
１３：シンボルクロック抽出器
１５：光ファイバ
１０１：波長分散補償回路
３００：受信装置 11: analog-digital converter 12: digital signal processor 13: symbol clock extractor 15: optical fiber 101: chromatic dispersion compensation circuit 300: receiver

Claims (8)

  1. 　光ファイバ伝送路の波長分散による波形歪みを補償する際の分散補償量を推定する波長分散量推定方法であって、
    　第ｋ（ｋは整数）番目の分散補償量Ｄ（ｋ）の初期値（ｋ＝０）である分散補償量Ｄ（０）を設定する初期値設定手順と、
    　受信データに含まれるシンボル到来タイミングクロックの分散補償量Ｄ（ｋ）における強度をクロック検出値Ｓ（ｋ）として検出し、記憶するクロック検出手順と、
    　前記分散補償量Ｄ（ｋ）を所定量ΔＤのＭ（ｋ－１）分の１（Ｍは１以上の実数）だけプラス側にシフトした分散補償量Ｄ（ｋ）＋ΔＤ／Ｍ（ｋ－１）における前記シンボル到来タイミングクロックの強度をクロック検出値Ｓ（ｋ＋）として検出し、記憶するプラス側シフト手順と、
    　前記分散補償量Ｄ（ｋ）を所定量ΔＤのＭ（ｋ－１）分の１だけマイナス側にシフトした分散補償量Ｄ（ｋ）－ΔＤ／Ｍ（ｋ－１）における前記シンボル到来タイミングクロックの強度をクロック検出値Ｓ（ｋ－）として検出し、記憶するマイナス側シフト手順と、
    　前記クロック検出値Ｓ（ｋ）、前記クロック検出値Ｓ（ｋ＋）及び前記クロック検出値Ｓ（ｋ－）を比較する比較手順と、
    　前記比較手順の結果、前記クロック検出値Ｓ（ｋ）が最大である場合、前記分散補償量Ｄ（ｋ）を最適分散補償量として決定して前記分散補償量の推定を完了し、前記クロック検出値Ｓ（ｋ＋）又は前記クロック検出値Ｓ（ｋ－）が最大である場合、最大の前記クロック検出値の前記分散補償量を第ｋ＋１番目の分散補償量Ｄ（ｋ＋１）として前記クロック検出手順、前記プラス側シフト手順、前記マイナス側シフト手順及び前記比較手順を再度行うことを決定する判定手順と、
    を行うことを特徴とする波長分散量推定方法。     A chromatic dispersion amount estimation method for estimating a dispersion compensation amount when compensating for waveform distortion due to chromatic dispersion in an optical fiber transmission line,
    An initial value setting procedure for setting a dispersion compensation amount D (0) that is an initial value (k = 0) of the kth (k is an integer) th dispersion compensation amount D (k);
    A clock detection procedure for detecting and storing the intensity at the dispersion compensation amount D (k) of the symbol arrival timing clock included in the received data as the clock detection value S (k);
    The dispersion compensation amount D (k) is a predetermined amount [Delta] D of M (k-1) worth of 1 (M is one or more real) dispersion compensation amount is shifted to the positive side by D (k) + ΔD / M (k-1 ) In which the symbol arrival timing clock is detected as a clock detection value S (k +) and stored.
    The symbol arrival timing clock at a dispersion compensation amount D (k) −ΔD / M (k−1) obtained by shifting the dispersion compensation amount D (k) to the minus side by a factor of M (k−1 ) of the predetermined amount ΔD. A negative shift procedure for detecting and storing the detected intensity as a clock detection value S (k−);
    A comparison procedure for comparing the clock detection value S (k), the clock detection value S (k +) and the clock detection value S (k−);
    If the clock detection value S (k) is the maximum as a result of the comparison procedure, the dispersion compensation amount D (k) is determined as the optimum dispersion compensation amount, and the estimation of the dispersion compensation amount is completed, and the clock detection When the value S (k +) or the clock detection value S (k−) is the maximum, the clock detection procedure with the dispersion compensation amount of the maximum clock detection value as the (k + 1) th dispersion compensation amount D (k + 1), A determination procedure for determining to perform the plus shift procedure, the minus shift procedure, and the comparison procedure again;
    A chromatic dispersion amount estimation method characterized by:
  2. 　前記初期値設定手順の前に前記分散補償量の概略値を取得し、前記分散補償量の概略値を前記初期値設定手順における前記分散補償量Ｄ（０）とする概略分散補償量取得手順を有することを特徴とする請求項１に記載の波長分散量推定方法。 Before the initial value setting procedure, an approximate value of the dispersion compensation amount is acquired, and an approximate dispersion compensation amount acquisition procedure in which the approximate value of the dispersion compensation amount is the dispersion compensation amount D (0) in the initial value setting procedure The chromatic dispersion amount estimation method according to claim 1, further comprising:
  3. 　前記クロック検出手順、前記プラス側シフト手順及び前記マイナス側シフト手順の少なくとも１つは、異なる時刻に複数回繰り返して平均化することを特徴とする請求項１又は２に記載の波長分散量推定方法。 The chromatic dispersion amount estimation method according to claim 1, wherein at least one of the clock detection procedure, the plus side shift procedure, and the minus side shift procedure is averaged by repeating a plurality of times at different times. .
  4. 　前記プラス側シフト手順及び前記マイナス側シフト手順で前記分散補償量をシフトする前記所定量ΔＤより小さい微少量δＤが設定されており、
    　前記クロック検出手順において、前記分散補償量Ｄ（ｋ）におけるクロック検出値Ｓ（ｋ±０）、及び前記分散補償量Ｄ（ｋ）を中心として分散補償量Ｄ（ｋ）±ｎδＤ（ｎは自然数）におけるクロック検出値Ｓ（ｋ±ｎδ）を検出し、
    　前記プラス側シフト手順において、前記分散補償量Ｄ（ｋ）＋ΔＤ／Ｍ（ｋ－１）におけるクロック検出値Ｓ（ｋ±０＋）、及び前記分散補償量Ｄ（ｋ）＋ΔＤを中心として分散補償量Ｄ（ｋ）＋ΔＤ／Ｍ（ｋ－１）±ｎδＤ（ｎは自然数）におけるクロック検出値Ｓ（ｋ±ｎδ＋）を検出し、
    　前記マイナス側シフト手順において、前記分散補償量Ｄ（ｋ）－ΔＤ／Ｍ（ｋ－１）におけるクロック検出値Ｓ（ｋ±０－）、及び前記分散補償量Ｄ（ｋ）－ΔＤを中心として分散補償量Ｄ（ｋ）－ΔＤ／Ｍ（ｋ－１）±ｎδＤ（ｎは自然数）におけるクロック検出値Ｓ（ｋ±ｎδ－）を検出することを特徴とする請求項１又は２に記載の波長分散量推定方法。     A small amount δD smaller than the predetermined amount ΔD for shifting the dispersion compensation amount in the plus side shift procedure and the minus side shift procedure is set,
    In the clock detection procedure, the clock detection value S (k ± 0) in the dispersion compensation amount D (k) and the dispersion compensation amount D (k) ± nδD (n is a natural number) centering on the dispersion compensation amount D (k) ) To detect the clock detection value S (k ± nδ)
    In the plus side shift procedure, the dispersion compensation amount centering on the clock detection value S (k ± 0 +) and the dispersion compensation amount D (k) + ΔD in the dispersion compensation amount D (k) + ΔD / M (k−1) D (k) + ΔD / M (k−1) ± nδD (where n is a natural number) detects a clock detection value S (k ± nδ +),
    In the minus side shift procedure, the clock detection value S (k ± 0−) in the dispersion compensation amount D (k) −ΔD / M (k−1) and the dispersion compensation amount D (k) −ΔD are centered. 3. The clock detection value S (k ± nδ−) in the dispersion compensation amount D (k) −ΔD / M (k−1) ± nδD (n is a natural number) is detected. Chromatic dispersion amount estimation method.
  5. 　クロック検出値Ｓ（ｋ±０）及びクロック検出値Ｓ（ｋ±ｎδ）を平均化して前記クロック検出値Ｓ（ｋ）とし、
    　クロック検出値Ｓ（ｋ±０＋）及びクロック検出値Ｓ（ｋ±ｎδ＋）を平均化して前記クロック検出値Ｓ（ｋ＋）とし、
    　クロック検出値Ｓ（ｋ±０－）及びクロック検出値Ｓ（ｋ±ｎδ－）を平均化して前記クロック検出値Ｓ（ｋ－）とする
    ことを特徴とする請求項４に記載の波長分散量推定方法。     The clock detection value S (k ± 0) and the clock detection value S (k ± nδ) are averaged to obtain the clock detection value S (k),
    The clock detection value S (k ± 0 +) and the clock detection value S (k ± nδ +) are averaged to obtain the clock detection value S (k +),
    5. The chromatic dispersion amount according to claim 4, wherein the clock detection value S (k ± 0−) and the clock detection value S (k ± nδ−) are averaged to obtain the clock detection value S (k−). Estimation method.
  6. 　前記判定手順で、前記クロック検出値Ｓ（ｋ）と前記クロック検出値Ｓ（ｋ＋）との差及び前記クロック検出値Ｓ（ｋ）と前記クロック検出値Ｓ（ｋ－）との差が所定の閾値未満の場合、前記分散補償量Ｄ（ｋ）を最適分散補償量として決定して前記分散補償量の推定を完了することを特徴とする請求項１又は２に記載の波長分散量推定方法。 In the determination procedure, a difference between the clock detection value S (k) and the clock detection value S (k +) and a difference between the clock detection value S (k) and the clock detection value S (k−) are predetermined. 3. The chromatic dispersion amount estimation method according to claim 1, wherein when the value is less than a threshold value, the dispersion compensation amount D (k) is determined as an optimum dispersion compensation amount, and the estimation of the dispersion compensation amount is completed.
  7. 　前記光ファイバ伝送路から受信した光アナログ波形をデジタル信号に変換するアナログデジタル変換器と、
    　前記アナログデジタル変換器が出力する前記デジタル信号が持つ前記光ファイバ伝送路の波長分散による波形歪みを、請求項１から６のいずれかに記載の波長分散量推定方法で推定した前記分散補償量で補償するデジタル信号処理器と、
    　前記アナログデジタル変換器が出力する前記デジタル信号に含まれる受信データのシンボル到来タイミングクロックを抽出し、前記シンボル到来タイミングクロックの強度を前記クロック検出値として出力するシンボルクロック抽出器と、
    を備える波長分散補償回路。     An analog-digital converter that converts an optical analog waveform received from the optical fiber transmission path into a digital signal;
    7. The dispersion compensation amount estimated by the chromatic dispersion amount estimation method according to claim 1, wherein a waveform distortion due to chromatic dispersion of the optical fiber transmission line of the digital signal output from the analog-digital converter is calculated. A digital signal processor to compensate;
    A symbol clock extractor that extracts a symbol arrival timing clock of received data included in the digital signal output by the analog-digital converter and outputs the intensity of the symbol arrival timing clock as the clock detection value;
    A chromatic dispersion compensation circuit comprising:
  8. 　請求項７に記載の波長分散補償回路を含む受信装置。 A receiving device including the chromatic dispersion compensation circuit according to claim 7.
PCT/JP2012/052318 2011-02-01 2012-02-01 Wavelength dispersion amount estimation method, wavelength dispersion compensation circuit, and reception device WO2012105628A1 (en)

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